A conventional travel assistance apparatus is installed in a vehicle to assist travel by the vehicle. To assist travel by the vehicle, the travel assistance apparatus determines behavior of the vehicle on the basis of various characteristics of the vehicle. Here, the various characteristics of the vehicle include characteristics that vary in accordance with travel conditions. Apparatuses described in Patent Document 1 to Patent Document 3, for example, are available as apparatuses that detect these varying characteristics of the vehicle. Patent Document 1 describes a system that calculates a travel energy of a vehicle. This system determines the travel energy by calculating a gradient resistance, an air resistance, an acceleration resistance, and a rolling resistance on the basis of an estimated travel speed, parameters relating to the vehicle, and parameters relating to a road. Patent Documents 2 and 3 describe apparatuses that estimate a weight of the vehicle.
Patent Document 1: Japanese Patent Application Publication No. 2011-016465 (JP 2011-016465 A)
Patent Document 2: Japanese Patent Application Publication No. 2007-271282 (JP 2007-271282 A)
Patent Document 3: Japanese Patent Application Publication No. 2002-81989 (JP 2002-81989 A)